These are built-in "difference amplifier". You can replace them with two identical NPNs connected as shown I believe, though you may need to get the specs close enough. Maybe a good result could be expected from an opamp actually?

In a thread here, Dirk mentions that the FL5 is a dead-on copy, I'll take some gut shots to post in the other thread and check for any replacement part...

I just got an FL-301DX (9V) on Monday (2nd one I've owned). It has a really noisy 'swoosh' (like air blowing), but the flanging works fine, so I opened it up to have a look. It also runs the MN3207. After taking hi-res shots of the solder side, I noticed the layout is VERY similar (about 80-85%) to the FL9. I'd bet good money that the only major difference in the FL9 is the addition of the Delay knob.

My vintage/MIJ FL9 has some kind of grounding issue where the LED stays slightly on when bypassed, causing any true-bypass pedal attached to it to pop when switched on/off. I'm recreating the PCBs in Illustrator (should fit in a 125-B), so I'll have a better idea of them in a week or two. Ideally, I'd like to build new ones minus the buffer/switching and compare them back to back.

Your problem description gives me the suggestion there is a resistance between the GND connection of the power supply and the GND on the PCB. This causes the circuit GND to float compared to the power supply GND and causes the output to have a DC offset. Hence the pops on other pedals.